Commercial airlines and military agencies spend large sums in periodically stripping or abrading paint and other coatings from the exterior surfaces of modern aircraft. These surfaces comprise light weight aluminum or other metal alloys, composites, or plastics, which are relatively soft and from which paint or other coatings must be carefully removed to avoid excessive abrasion or chemical damage. Such damage may, in extreme cases, lead to mechanical failure.
Blasting media useful for removing coatings from sensitive metal and composite aircraft or like surfaces should, preferably, meet the following criteria:
1. They should be relatively non-aggressive (Mohs hardness of about 2.0-3.0);
2. They should be available in various particle size distributions for the treatment of different substrates;
3. They should be free-flowing under high humidity conditions and throughout a broad range of air pressure and media flow rates;
4. They should be water soluble and non-polluting to facilitate easy separation from the insoluble paints and resins stripped to facilitate waste disposal; and
5. They should be non-corrosive to substrates and adjoining surfaces contacted by the blasting media.
Sand blasting, the principal means for cleaning or stripping hard durable surfaces such as granite or heavy steel plating, is too abrasive for removing coatings from sensitive substrates. Blasting techniques have therefore been used on sensitive substrates that employ materials softer than sand, such as plastic materials, walnut shells, and corn cobs. The disadvantages of these softer materials are that they are insoluble and therefore not easily disposable. Additionally, plastics are also expensive.
A blasting medium for removing coatings from sensitive substrates containing water-soluble bicarbonate particles, preferably sodium bicarbonate, having average particle sizes of 100 to 500 microns, in admixture with a hydrophobic silica flow/anti-caking agent, has been developed by the owners of the present invention as taught in U.S. application Ser. No. 07/323,412 (International Application No. PCT/US90/04203), U.S. application Ser. No. 07/506,447, and U.S. application Ser. No. 07/702,049. Although effective in removing coatings from substrates, the larger particle sizes of bicarbonate makes it a less efficient blasting medium than blasting media employing compounds with small particle sizes, such as fine sand, which have better cutting efficiencies. Additionally, more water is needed to wash away the waste produced by bicarbonate-containing blasting medium than is generally used in commercial blasting systems because of the relatively low solubility of bicarbonate in water.